There's a little extra feature on my car that I have yet to see on another TVR Wedge...


Yes, it's cruise control! I don't know if it was ever offered by TVR as an option (I doubt it!), but I thought it may come in useful for those long drags down the motorway when my right foot has a habit of getting carried away with itself...;-)

In the same way that the fuel injection system was an 'add-on' for the SD1 (and the Range Rover), the Hella GR65 cruise control system is a fairly simple collection of components that can be easily liberated from a donor SD1. One or two items are not so obvious and may be harder to get at, but if you do as I did and buy a system already removed from the donor car, the hard work is done and you just need to make sure all the bits are there! In my case they weren't, but more of that later...

So, what's involved? The cruise control works quite simply: you get to a speed that you'd like to maintain, press a switch and the car maintains that speed. You can over-rule the cruise by accelerating (say, to overtake something) and certain safety features are included to stop you doing something that could break the car, or yourself!

1. First off, you need a cruise ECU. Packed with digital electronics (in a 1980's sort of way!) the ECU performs the calculations of road and engine speed and sends signals to the vacuum system to adjust the throttle.

2. Vacuum system? Yep, there's a miniature vacuum pump and solenoid valve that creates and controls the vacuum necessary to operate...

3. The vacuum servo (or 'bellows'); which is linked to the throttle assembly by... well, a bit of stiff wire! This was improved later to a slotted link and can be found more easily on Range Rovers as more of them had cruise control.

4. Of course the ECU needs to know how fast the car is travelling; this is measured by a sensor mounted on the gearbox that detects the rotation of the propshaft - now this is my main sticking point, since the sensor drove the electronic speedo of the SD1 in place of the cable-driven version. The older (Dana) cruise system uses a small magnet mounted to the output flange of the gearbox; as it passes the sensor a pulse is generated that is fed to the ECU. The faster the prop turns, the faster the car is going and the more pulses are generated (when I started looking into installing cruise I thought I may have to adapt this idea to drive the Hella system, as the TVR of course uses a cable-driven speedo). I didn't get the Hella's pulse generator with the rest of the system, but managed to source another via Ebay.

5. Steering column control switch. As seen in the picture above. Tells the ECU when the cruise is required, when it's not, and when it is again. More or less. Quite a neat solution, from a retro-fitting point of view. A lot of cruise-equipped cars had/ have the cruise functions selected by switches in the steering wheel, so you need to change the steering wheel. Luckily BL were cheapskates and did it this way instead :D The only minor change was to the upper column shroud, which has a new cutout to suit the cruise switch. It wouldn't be absolutely essential to have this shroud from the donor, as the existing one could be modifed with care. The cruise switch has its own mounting bracket which screws to two holes thoughtfully provided in the rear of the indicators/dip/main/horn switch, so again, as long as you get the cruise switch itself, the existing switchgear can be retained - as long as your TVR still has SD1 switchgear, that is. I have actually seen a couple of TVR Wedges with the modified upper shroud, but no cruise. I guess TVR fitted whatever they could lay their hands on that week... ;)

6. Overspeed relay. Detects ignition pulses and cuts the cruise if the engine revs exceed a certain point: this stops you engaging cruise in a low gear and over-revving the engine trying to get there! I think the limit for the V8 is 5400 pm, which in the TVR would be something on the wrong side of 125 mph in top...

7. Pedal switches. Fitted to the brake and clutch, these are cut-out switches that tell the ECU to release the vacuum if either pedal is depressed (braking, or changing gear...) as otherwise the engine would rev to the skies, or try to fight the brakes. As well as an electrical contact, the switches also incorporate a valve that opens the vacuum line to atmosphere, rapidly releasing the vacuum servo so the throttle closes quickly, as opposed to switching the cruise off by the column switch which slowly releases the vacuum to slow the car smoothly. Some thought will have to be given to how best to mount the switches on a Wedge as the pedal box wasn't designed with cruise control in mind.

8. Wiring loom and main fuse - as it says, a dedicated section of wiring with all the necessary connectors and fuse to supply the components of the cruise system.

A selection of brackets were also used to mount the cruise components on the original car; some ingenuity may be necessary to adapt them for Wedge fitment (or they may of course be junked in favour of new hardware).

More pictures to follow as and when I get chance...

Update 24/08/06

I finally got around to assembling the cruise components and establishing that they work... OK so it took a bit of thinking about - I bypassed the overspeed relay; one wire has to be earthed to simulate connection via the brake lamps - some sort of safety feature; the speed pulse generator needs a load resistor as the electronic speedometer isn't present... but apart from that it works!

I used a cordless drill to spin the pulse generator; pressing the 'SET' switch caused the vacuum pump to fire up and suck the bellows unit. Speeding up or slowing down the drill made the bellows extend or retract just as it should.

So, how to fit the bits to the car? The column switch was far and away the easy bit! The pedal box will have to come out, which means dropping the steering column, the clutch master cylinder and half the wiring loom... but first I considered the bellows unit. There are two obvious points where the bellows could pull on the throttle linkage, but only one of them seems to allow a proper arc of travel. So with a bit of measuring and some guesswork, a piece of steel plate was cut and drilled to support the bellows off the side of the existing steel bracket, using two bolt holes thoughtfully provided:

The TVR uses THREE throttle return springs. I wondered whether the vacuum pump and/or bellows would be able to pull the throttle against such resistance. Firstly I tried sucking on the bellows and that seemed to work OK, so I temporarily connected up the pump and applied power. It worked!


Finally, I checked to make sure that the throttle linkage could work through its full range without the cruise linkage fouling it. All OK there. There was a slight flexing of the new bracket but not enough to prevent the bellows working; later I added a welded gusset to stiffen the bracket.

Next I pondered whereabouts to site the vacuum pump. I settled on the inboard side of the GRP moulding that surrounds and supports the pedal box. This position keeps the pump out of the way of just about anything that I'd be likely to need access to, whilst leaving it handy for electrics and vacuum pipework. I tried the original mounting bracket every which way but couldn't make it fit so I gave up and fabricated one - a simple L-shaped affair - with captive threads for the pump mounting screws.


Update 31/08/06

It was time to take a deep breath and get stuck in. There was no other way: the pedal box would have to come out. There was no way I was even going to attempt to weld brackets to it, down in the depths of the footwell. Luckily I had a couple of days off work. It looked like I might need them...

As it turned out, it wasn't all that difficult a job. Before you can extract the pedal box, the steering column needs to come out. This means disconnecting the upper universal joint in the wheelarch. Disconnect all the multiplugs from the column switchgear (snipping cable ties as you go!), remove the two nyloc nuts holding the clamp to the support strut and the column should drop onto the driver's seat. At first glance it looks as though you could unscrew the column clamp knob from the rake/ tilt assembly and drop the column that way, but there's a cunningly-placed roll pin to stop you removing the clamp bolt. Once I had the column out I knocked this out and replaced it with a split pin in case I ever need to drop the column again. Here's the roll pin:


The column with it's mounting and rake/tilt clamp:


Eagle-eyed readers will spot that the lights switch appears to be upside-down: you can pull the lever off and invert it! The rusty elliptical thing at bottom left is the bush that supports the column where it passes through the footwell; there's a bit of play so it needs replacing. More on that here...

Four nuts hold the pedal box to the brake servo; two more secure the clutch master cyl.; two bolts hold the box to the scuttle (the ones just above & behind the brake servo when seen from the engine bay). Two of the servo nuts retain the throttle pedal on a separate bracket; the throttle cable needs to come out as does the bonnet release cable and the speedo cable. With the clutch and brake pushrods unclipped from the pedals and the brake light switch wires detached, it was just a matter of wriggling the pedal assembly out from under the dash (apologies for the chav-tastic pedals, previous owner's doing!):


Although the steelwork had been plastic-coated there were a few patches where clutch fluid leaks had removed the coating. I took the opportunity to sandblast and repaint these areas and also the pedals themselves. I played around with the cruise release switches and fabricated some simple brackets (in the style of the existing brake lamp switch one!) to locate them. These were duly welded and painted, then the unit reassembled with fresh grease.

The white switch is the brake lamp switch and the other two are different versions of the Hella release switch. The simple strap brackets allow the switches to be adjusted relative to the pedals.

Whilst the paint was drying I took the opportunity to mount the vacuum pump using self-tappers, with a smear of silicon sealant to keep the water out:-


The vacuum servo almost looks original! I got my paint cans mixed up: the finish was supposed to be satin black, not matt! You can see the slotted link that allows free movement of the throttle linkage when not in cruise mode:-

Update 15/08/08:-

The remaining stumbling-block to cruise-controlled Nirvana had, for some time, been the lack of electronic pulses that the cruise ECU needs to know the vehicle's speed. The earlier SD1s (and the TVR) used a cable-driven speedometer, whereas the later SD1s gained an electronic instrument pack that included fuel economy information. This used a sealed pulse generator that was fitted to the gearbox in place of the cable drive. I could use one of those but then I'd lose my speedo. I'd seen a couple of later TVR wedges that used an electronic pulse generator fitted in-line with the speedo cable, but they were used to feed speed information to the fuel injection system ECU to aid the idle stabilisation. Then I discovered that some Range Rovers used the same pulse generator either for cruise control or just to drive an electronic speedometer, so of course I HAD to get hold of one to try. One rummage on Ebay later and the pulse generator was installed to the system and spun-up with a cordless drill. It worked! The SD1 electronic generator normally used with the Hella cruise system is a 'proper' sealed bit of electronics where the (Jaeger) device from the Range Rover is simply an 8-pole magnet spinning in close proximity to a reed switch. Whether this will cause issues with contact bounce will only become evident once I locate a suitable (split) speedo cable with which to complete the installation. Having plumbed the vacuum lines in (I used 5mm airline tube and push-fit connectors, should be OK for vacuum as the pump will compensate for any leaks!), the next stage will be to find space to locate the cruise ECU and overspeed relay and wire in the pedal switches.

Update 11/10/08:

Needless to say, the combination of LT77 gearbox and VDO instruments on the TVR results in a speedo cable that appears to be incompatible with anything from any car manufacturer in the known universe, let alone anything that would have a split cable! I'd heard about Speedy Cables so I fired off an email to see if they could make me something; the reply was positive enough that I chucked the old cable plus the speed transducer into a Jiffy bag and sent it winging Wales-ward. A fortnight later another Jiffy bag appeared (courtesy of my nosy neighbour who takes it upon himself to intercept any deliveries to my house should I not answer the door in 45 microseconds... could be useful if I ever receive any letter-bombs!) containing exactly the right bits to do the job! From my recollections of other Wedges I'd seen with the same speedo transducer, it was fitted into the cable in a position that left it in the engine bay. I asked Speedy Cables to position it just a few inches from the speedometer end so that it'd remain in the cabin. At time of writing it's a bit late in the evening to start dragging the car out and squeezing my not-inconsiderable bulk under the dashboard, but I can safely say it looks as though the missing pieces of the Wedge cruise-control jigsaw are to hand and will be installed shortly... and all for £51. Bargain.

The only slight hiccup was with the knurled nut that secures the upper cable to the rear of the speedo: the nut was too deep and wouldn't pull the cable firmly against the speedo boss. A few seconds dressing with the bench grinder easily reduced the depth and the cable nipped up securely. Pic shows the cable before doctoring, it's the nut at left end of the short cable that needed work:

To make access easier I whipped out the split pin mentioned above and dropped the steering column onto the driver's seat. The lower bearing protested a bit as it had to move in its housing to accommodate the movement but it coped OK...

Update 12/07/09:-

It works! Having decided it was high time I had the old beast back on the road, I had to do a few jobs on the car in order to get an MOT (see elsewhere for lovely pics of rusty suspenders!). Once the formalities were out of the way and I was driving again, I kept noticing the various wires dangling under the dash and set about completing the cruise control installation. There wasn't much left to do; the ECU and overspeed relay were simply mounted (read: shoved) behind the centre radio console. This left the wiring loom nicely positioned so that it ended under the instruments. Once again the steering column was dropped and the handful of connections made. I had to run two wires across the cabin to the passenger footwell; one ties in to the ignition pickup feed that triggers the fuel injection and the other I spliced in to the boot lock fused feed (can't see me trying to 'cruise' and open the boot at the same time!). The brake and clutch pedal switches were wired in series; the column switch simply plugged in. Suddenly... it was finished! Time for a drive then. I took along the wiring diagram, multimeter and spare fuses but I needn't have worried. I hit the local dual carriageway and sat at about 40mph. I pulled the stalk towards me to energise the cruise system. Then I tapped it upwards to 'Set' and slowly lifted my foot off. With just a slight surge the cruise control took over and I was able to test the controls. Below about 35mph the throttle response gets a bit ragged, it's rather on/off, on/off... but that's hardly where you'd use cruise. Up at 70/80 mph it's spot-on. Mind you, exiting a roundabout in second gear and hitting 'Resume' when you were just doing 80 gets interesting... 8^0

Meanwhile, I'd pondered a few times over the spindly column switches that TVR robbed from the SD1. With the 390's smaller steering wheel, the stalks stuck out some way either side and the indicator lever was forever getting stuck against the radio console! What was needed, I thought, was some shorter stalks. Preferably not spindly. Preferably more 'in keeping' with the other cabin accessories, like the alloy gearshift knob and alloy handbrake. I know! I'll make some new stalks... out of alloy :^D

Now I'm by no means a skilled machinist so attempting to replicate the existing switches with their push-button ends for horn and screenwash was a non-starter. What I needed was some ready-made pushbuttons, around which I could design the 'stalk'. I duly found some stainless steel pushbuttons that have threaded bodies. Some aluminium bar was then bashed about on the lathe - drilled, turned, bored, knurled, threaded and generally reduced to swarf on the floor - resulting in these:



I think they're still a bit long (though they're an inch shorter than the SD1 originals) so now I know what I'm doing (ahem) I'll have another go. Of course I'll need to make another one for the cruise control as well! Here's the new switchgear on the car:

...and with the alloy gearshift and handbrake:

You know, I think those heater controls might look better in aluminium.... :^D

Update 15/08/12:

... and indeed they do (or at least they will when they're finished!).


The large holes are in response to someone who pointed out that I was adding excess weight to the car...!

Meanwhile, a fellow Wedge owner had spotted my alloy switchgear at a TVR meeting and persuaded me to make him some for his early Tasmin. The Tasmin used TR7 column switches and the levers were more bent than those on the SD1, but with some care I made these for him:


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